Question

State the conditions to get constructive and destructive interference of light.

Answer 1

Light travels in the form of transverse waves. It consists of crests and troughs.

When we consider two or more light rays they are said to be in phase when they are in the same state of vibration. Either both should be crests or both should be troughs.

They are said to be out of phase when they are in opposite state of vibration. One is crest and other is trough.

When two or more light rays arrive at a point in phase, they superimpose on each other and form a constructive interference. Their amplitude gets added up and a very bright light is observed at that point.

When two or more light rays arrive at a point out of phase, they superimpose on each other and form a destructive interference. Their amplitude gets subtracted and a darkness is observed at that point.